Tom Ramcigam (magicmarmot) wrote,
Tom Ramcigam

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Woke up this morning to a cold house. The boiler was again not working, so I quick threw on some clothes to head to the plumbing and heating store to get a new igniter/control assembly.

Backstory: when the gas man came last night, he told me that it was quite likely that the igniter module was bad, as there was a known problem with the control module. Instead of replacing it and charging me an arm and a leg, he made the call that it was a non-Minnegasco problem and didn't charge me at all, and I could get my own module and replace it.

As an aside, he was pretty impressed with the plumbing and control system. It is kind of impressive when you first see it. :)

So I got the updated igniter assembly and installed it.

Nothing. Flatlined. Fuuuuuck.

Okay, so Honeywell has replaced the old S8610M/F/L/D modules with one universal module, the S8610U. It has a few extra terminals, so I did some further research and discovered that there is a thermostat coneector on the module. I jumpered that, and she started sparking and lit up the pilot light.

Unfortunately, still no burners. Fuuuuuck.

Okay, the gas valve has three terminals. One is common, one turns on the pilot, and the third turns on the main gas valve. Just for a test, I jumpered the main gas valve, and it fired right up.

What this means is that the module isn't sensing that the pilot light is lit.

Okay, this is where it gets dicey. As far as I can tell, there is no sensor for the pilot flame. There is the ignitor and the gas tube from the gas valve and a third ground wire. That's it.

So I am suddenly stumped.

I managed to get the burner running fine so the system will actually go through at least one heat cycle and get the house warm again before it shuts off, so I'm at work. I took the old ignition module with me to open it up and see if I can determine how the damn thing senses a pilot flame so I have more understanding of why it's not working.

Half of research is finding the right terminiology. This is what I found:


  • The controller applies alternating voltage between the flame sensing rod and the base of the flame (ground)


  • The flame rod is positioned such that the high temperature sensing rod would be in contact with the flame.

  • The flame creates an ionized "path" between the center electrode/rod and the electrical ground.

  • The excitation voltage induces a current flow across this "path". This results in a very small DC offset current. DC offset is small, only micro amps.

  • This current is a stable, measurable signal which can then be used in the appropriate control scheme. If there is a flame present, the DC offset is detected by the controller, which tells the gas valve to remain open.

So the flame sensor is actually built into the ignition controller. The problem is very likely that my ignitor/flame sensor needs to be cleaned with some emery cloth to increase its conductivity.

Which also likely means that my old ignition module is just fine, and I didn't need to spend that extra $150 for a new one.

Ah, well, a spare isn't a bad idea.

I'll clean the ignitor/sensor when I get home tonight.
Tags: mcgyver, techgeek

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